ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



673 



Fig. 119. 



Schieck's Microscope with Large Stage.*— Prof. G. Fritsch 

 writes that F. W. Schieck deserves special commendation " for con- 

 structing stands which, in regard to the size of the stage, very 

 considerably exceed the ordinary dimen- 

 sions without being either clumsy or 

 unsightly. The ever increasing neces- 

 sity for examining preparations of large 

 size (such as sections of brain), or series 

 of preparations on large slides, make such 

 stages a pressing necessity." Fig. 119 

 shows one of these stands with a stage 

 14 cm. wide. To prevent the slide from 

 falling over the sides when moved to 

 the furthest extent, two arms are attached 

 to each side, the upper surface of which 

 is on a level with the stage. When not 

 required they can be turned back close to 

 the sides of the stage. 



Projection-Microscopes.! — Dr. Hugo 

 Schroder, in an interesting paper on 

 lantern or projection-Microscopes, points 

 out that the oldest forms originated in the 

 earliest times of microscopical observa- 

 tion, when the whole magnifying apparatus 

 consisted of a simple bi-convex lens with 

 very small aperture. In consequence, the 

 images had great depth, so that relatively 

 thick objects were shown with distinct- 

 ness. The images, however, by lamplight were exceedingly dim, if the 

 power amounted to 100 or more. This was not, however, the only 

 defect arising from the very small aperture, for the resolving power 

 was also very insignificant, and the image was injuriously affected by 

 the chromatic and spherical aberrations of the objective-lenses. As 

 the result of these and other defects, the instrument was so unsatis- 

 factory with regard to distinctness of detail that the 6ame 

 objective-lens was more efficient when used as a simple magnifying- 

 glass. 



It will therefore be naturally asked in what consists the usefulness 

 of the projection-Microscope ? 



Its utility is to be sought in quite another direction, and under 

 certain circumstances it becomes highly important, if not indispen- 

 sable. For purposes of demonstration there is nothing better than a 

 good projection-Microscope. Many persons can examine the object at 

 the same time, and a larger field of view can be obtained than would 

 be possible with any other combination. The angle of the image, 

 which in the compound Microscope is at most 10°, can be increased to 



* Berieht wiss. Instrumente Berliner Gewerbeausstellung im Jahre 1879 

 (L. Loewenberg, 1SS0) p. 293 (1 fig.). 



t Cential-Ztg. f. Opt. u. Mech., iii. (1SS2) pp. 2-4, 15-17 (1 tig.). 



